1. Field of Invention
The present invention relates to an inductor, and more particularly to an inductor for a substrate of a circuit board.
2. Related Art
Accompanying to the development of semiconductor device and process, the inductor required in a circuit of voltage control oscillator (VCO) or radio frequency processor (RF processor) can be directly formed in a chip or be formed in a microstructure and integrated with a chip. The circuit of VCO or RF processor is correctly and stably operated with the inductor of desirable inductance and high quality factor. The quality factor is defined as follows:The quality factor≈(energy stored/energy lost).
As shown in FIGS. 1 to 3, a conventional inductor 1 includes a plurality of electrical conductive layers 11-14 disposed over a substrate 2. Between the substrate 2 and the electrical conductive layers 11-14 are isolated by a dielectric material (not shown). The electrical conductive layers 11-14 are electrically connected with each other via a first end 15 of the inductor 1 and the electrical conductive layers 11-14 are electrically connected with each other via a second end 16 of the inductor 1. Two signal terminals (not shown) are respectively connected with the first end 15 and the second end 16.
The inductor 1 is formed to be a multiple spiral structure for increasing an effective cross-sectional area to lower the series resistance, the loss is thus degraded and the quality factor is thus raised. However, the quality factor is influenced by parasitic capacitances between the electrical conductive layers 11-14, parasitic capacitances between the electrical conductive layer 11 and the substrate 2, and eddy current induced in the substrate 2. Thus, the storage capacity of the inductor 1 is lowered under application of high frequency, especially in conductive silicon substrate of an integrated circuit.
It is therefore an important subject of the present invention to provide an inductor with high quality factor to reduce the influence of eddy current of the substrate and parasitic capacitance between the inductor and the substrate on the quality factor, and improve the efficiency and quality.